A phased array antenna technique has been widely used in the field of wireless communication and radar. When the technique is applied to a transmission apparatus, formation of beam directionality and electronic scanning of a beam are enabled. In the field of wireless communication, for example, a beam is formed to improve the antenna gain and scanned with the result that the range of communication area can be widened, or the cover area can be dynamically controlled in a base station in accordance with the number of accommodated users. In an application to a radar, when a beam of high directionality formed by a phased array antenna is radiated to a detection object from a transmission apparatus, furthermore, it is possible to suppress reflection (clutter reflection) from a non-detection target, and there is an effect of improving the detection accuracy with respect to the position of an object.
In a transmission apparatus using a phased array antenna technique, a plurality of antenna elements are arranged in an array form, and the phases and amplitudes of a plurality of parallel transmission systems (hereinafter, referred to as “transmission branches”) which supply electric power to the respective antenna elements are adequately controlled, whereby a desired directionality gain as an antenna can be obtained. In each transmission branch, the phase and the amplitude must be accurately controlled. When an error occurs in the phase or the amplitude, for example, the shape of a beam is collapsed, and therefore the antenna gain of the main beam is lowered, or a strong radiation beam is formed in an unwanted direction, thereby causing degradation of the system characteristics.
In wireless transmission using a phased array antenna, in the case where an error occurs in control of amplitudes and phases between transmission branches, it is requested to provide a technique for correcting the error. The error may be caused by various factors such as performance variations of components used for circuit mounting, unevenness of processes for integrated circuits, variations due to usage environments (for example, the temperature), or performance variations of power sources used in respective transmission branches.
In wireless transmission using a phased array antenna, as a technique for correcting a phase error and an amplitude error, for example, related art examples disclosed in Patent Literatures 1 to 3 are known.
The array antenna transmission and reception apparatus of Patent Literature 1 has a configuration where RF transmitters (wireless transmitters) which supply electric power respectively to a plurality of antennas are disposed to form a beam. RF receivers for calibration (wireless receivers for calibration) which detect amplitude and phase errors of respective transmission branches, a fast Fourier transformer, and a calibration value measuring section are separately disposed. In order to realize error correction, transmission signals of the respective transmission branches which are extracted by a changeover switch are sequentially received and processed to calculate a calibration value for error detection and correction. Then, a feed back to the respective transmission branches is performed based on the calculated calibration value, thereby correcting the phase error and the amplitude error.
The communication apparatus of Patent Literature 2 operates in a similar manner as that of Patent Literature 1. In a calibration section for detecting amplitude/phase errors of respective transmission branches, an RF·IF section (radio frequency/baseband frequency converter), a detector, and a calibration weight calculator are separately disposed. Transmission signals of the transmission branches which are extracted by a coupler are sequentially received and processed, a calibration value for error detection and correction is calculated, and the error is corrected.
The phased array antenna device disclosed in Patent Literature 3 includes: a correction phase storage device which stores correction phase information; and a correction phase indicating circuit which acquires information relating to a delay time of each real-time delay phase shifter, and which indicates a correction phase according to the delay time of each real-time delay phase shifter, and corrects a phase error between respective transmission branches by the phase shifter and a delay device.